1. Field of the Invention
A flueless, low nitrogen oxides, low carbon monoxide space heater in which a swirling fuel flow mixes with a counter-swirling primary airflow with respect to the swirling fuel flow, to form an intimately mixed fuel/air mixture. The flueless space heater admits secondary air into an upper portion of the combustion chamber for additional quenching, continuous combustion, and dilution, thus reducing or eliminating nitrogen oxides and carbon monoxide emission.
2. Description of the Prior Art
The basic principles used to reduce or eliminate nitrogen oxides and carbon monoxide emissions through combustion, quenching, post burning, and dilution are known to the art. Burned with theoretical quantity of air, a methane-type gaseous fuel having a combustion temperature of approximately 3450.degree. F. and an ignition temperature of approximately 1200.degree. F. will produce dangerously high levels of nitrogen oxides in an uncontrolled burning situation. Given such conditions, an unvented space heater will produce high levels of nitrogen oxides. In comparison, kerosene vapors surrounding a wick in a similar unvented space heater will ignite at approximatelY 700.degree. F. The low ignition temperature of the kerosene vapors effectively inhibits the formation of nitrogen oxides in such heaters.
In large industrial-type applications, an operating engineer has the freedom to control and adequately mix a fuel and oxidant, providing the residence or burnout time, and the staged quenching to satisfy the theoretical requirements of low nitrogen oxides production by conventional means. However, it is not immediately apparent that the low emissions of nitrogen oxides in kerosene wick-type heaters can be duplicated by a natural gas or other gaseous fuel burning appliances having a similar design, size and rating.
Reich, U.S. Pat. No. 3,689,040 teaches a low carbon monoxide, high heat output, portable gas heater of the type swept by a high velocity airstream, such as used on construction sites. The gas burner may have fuel gas introduced obliquely providing a fuel swirl into a primary combustion chamber. Air is drawn into the primary combustion chamber through holes in a peripheral chamber wall. A downstream secondary combustion chamber is formed by a conical flange extending from the open end of the primary combustion chamber. A baffle plate extends over a large portion of the flange opening with secondary combustion air being admitted through holes in the flange. The holes are spaced outwardly from the baffle. If natural gas is used as a fuel, a further circle of smaller holes is provided at or near the edge of the baffle. The '040 patent teaches two-stage combustion but does not disclose a counter-swirling introduction of primary combustion air to mix with the fuel. The '040 patent does not teach any decrease in nitrogen oxides emissions.
Voorheis, U.S. Pat. No. 4,488,869 teaches a high efficiency, low nitrogen oxides emitting, staged combustion burner for gaseous, liquid or pulverized solid fuels. The burner is self-contained and primarily used in smaller furnaces, as opposed to large industrial furnaces, which provide low nitrogen oxides by staged combustion with introduction of swirling primary air and introduction of fuel straight along the central axis of the main combustion chamber which is in the self-contained burner. The self-contained burner also introduces secondary air at its downstream end in a direction to converge on its axis and to also provide a spin, the combination maintaining a cylindrical-shaped flame. Primary air is introduced at about 75 percent of stoichiometric and a provision is made for a short residence time in the primary combustion zone which is entirely within the burner basket.
Vache, U.S. Pat. No. 4,105,013 teaches a portable stove having a replaceable pressurized combustible gas cartridge, a burner head, and framework for supporting a cooking vessel. Vache, U.S. Pat. No. 4,192,284 also teaches a portable stove fueled by pressurized gas.
A publication by Lawrence Berkeley Laboratory, University of California, Applied Science Division, "A Comparative Study of Combustion in Unvented Space Heating Devices", by T. Lionel, R. J. Martin and N. J. Brown, presented at the Western States Section/The Combustion Institute 1984 Fall Meeting, Stanford University, Stanford, Calif., Oct. 22-23, 1984, teaches wick-kerosene heaters and compares multi-stage, radiant, and convective configurations. The publication relates primarily to kerosene heaters and the concentrations of nitrogen oxides and carbon monoxide emissions associated with such kerosene heaters.